My invention relates to a process for making high purity p-xylene and, more particularly, for making p-xylene with a purity of at least 99.8% by weight from a crude product obtained by crystallization whose purity is about 98% by weight.
Crystallization methods can be used to separate p-Xylene from a C.sub.8 -aromatic starting material which contains ethyl benzene as well as the three xylene isomers. Use is made of the fact that the melting point of the individual C.sub.8 isomers have significant temperature differences. However conventional crystallization methods can be used to make p-Xylene with a purity of greater than 99.5% by weight only with great expense. Thus p-Xylene which was produced in a centrifuge without additional processing with a purity of about 98% by weight is subsequently treated to produce p-Xylene with a purity of over 99.5% by weight in the centrifuge with final products or with suitable media for that which may be separated by distillation from p-Xylene.
Currently p-Xylene with a purity of over 99.8% by weight made by a special adsorption process has been marketed which naturally caused corresponding inquiries about this very pure product.
With the help of crystallization processes up to now however only with great expense and Xylene loss has a p-Xylene product of comparable purity been made so that for the professional engineer a plant operating according to the crystallization process is at a genuine competitive disadvantage.